Picking apart RAID

Disk striping

No

The data is broken down into blocks, and each block is written to a separate disk. Since the I/O load is spread across each disk, this RAID level performs efficiently both reading and writing data to and from the array.

Low

2

When one drive fails, the entire array is compromised.

Disk mirroring

No

All data is duplicated on both disks. This RAID level requires an even number of disks.

Very high

2

When both drives fail, the data is lost.

Hamming Code ECC

No

There are two sets of drives: data drives and ECC drives. Each data word has its ECC data recorded on ECC disks.

Very high

2

Because of its ECC encoding method, it is very inefficient and expensive. RAID 2 is not commercially accepted.

Parallel transfer disks with parity

Yes

Data sector is subdivided and distributed across all data disks. Redundant information is stored on a dedicated parity disk.

(N-1) disks

Very high

3

When more then one drive fails, the array is compromised.

Independent data disks with shared parity blocks

Yes

Each block is written onto a data disk. Parity for same rank blocks is generated on Writes, recorded on the parity disk, and checked on Reads.

(N-1) disks

Very high

3

When more then one drive fails, the array is compromised.

Independent access array without rotating parity

Yes

Data sectors are distributed as with disk striping. Redundant information is interspersed with user data.

(N-1) disks

Very high

3

When more then one drive fails, the array is compromised.

Independent Data disks with two independent distributed parity schemes

Yes

Like RAID 5, parity is striped across the disks in RAID 6. However, in RAID 6, parity is written twice.

(N-2) disks

Very high

3

Depends on implementation, although I know of no RAID 6 implementations.